The present invention relates to valvetrains of internal combustion engines; more particularly, to devices for controlling the open duration of valves in such valvetrains; and most particularly, to a system for selectively varying the point at which the intake valves close in an internal combustion engine.
Many advances have been made recently toward reducing the emissions and increasing the efficiency of Diesel engines. One such advancement has been the development of Homogeneous Charge Compression Ignition (HCCI) systems. HCCI is a process wherein an initial premixed, homogeneous charge of Diesel fuel and air is compressed and partially burned by high temperature and pressure in a flameless process, followed by one or more post injections of fuel, as opposed to classic Diesel ignition wherein a charge of air is compressed and then injected with Diesel fuel, resulting a stratified mixture of fuel and air. HCCI has yielded many benefits including extremely low emissions of NOx and particulate matter (soot) because of lower ignition temperatures and the use of a leaner fuel/air mixture.
However, HCCI has its challenges. For example, with a compression ratio in the range of 9:1 to 14:1, starting an HCCI-ignited engine in cold weather can be difficult. This challenge can be addressed by selectively varying the point at which the intake valves close during the engine cycle to controllably reduce the compression ratio from that of a higher designed value, optimized for cruising conditions. By selectively keeping the intake valve open for a portion of the compression stroke, a portion of the volume of air that would otherwise be compressed in the cylinder by the up-moving piston, is instead bled back through the open intake valve, thereby effectively reducing the compression ratio on the engine.
Mechanization of an HCCI strategy that can selectively vary the compression ratio has been proposed in the past with limited success because of system and hardware complexity. For example, mechanization has been achieved by using two separate cam phasers to operate two intake valves at each cylinder so that intake valve opening and intake valve closing can be controlled by the phasers independently. Although effective, the use of two cam phasers is costly, adds weight to an engine and vehicle and often cannot be fitted into available space.
What is needed in the art is a simplified mechanism for selectively varying the closing point of the intake valves of an HCCI engine that is relatively easy to manufacture and assemble, has few parts, and requires minimal packaging space in an engine envelope.
It is a principal object of the present invention to provide variable closing timing of intake valves of an internal combustion engine.
It is a further object of the invention to simplify the manufacture and assembly of a system for such variable closing timing.
Briefly described, a Continuously Variable Valve Duration (CVVD) system in accordance with the invention includes a rocker assembly acted upon by first and second cam lobes disposed on first and second off-spaced intake camshafts, respectively, for selectively varying the closing point of the poppet valves, for example, the intake valves, in an internal combustion engine. As disclosed below, the present invention is described in terms of the engine intake valves, but it should be understood that the invention is also applicable to engine exhaust valves as well, or to both intake and exhaust valves as may be desired.
The opening camshaft is rotatably driven by the engine crankshaft and controls conventionally the opening point of the valves through a novel rotatable rocker assembly disposed on a fixed rocker pivot shaft.
The closing camshaft is rotatable and is connected to the engine crankshaft through a cam phaser device driven preferably by a gear train from the opening camshaft. The closing cam lobe is poised to take over control of the closing event of the valves through the same rotatable rocker assembly. By changing the rotational phase of the closing camshaft relative to the opening camshaft via the cam phaser, the phase of the closing camshaft can be advanced or retarded relative to the opening camshaft to take over the closing event of the valves. By doing so, the point at which the valves close in the cycle can be selectively varied over a wide range of open times. Additional embodiments for adapting the CVVD system to various valvetrain types are provided.
An important advantage of the present device is its simplicity. With the rocker assembly being rotationally mounted on a fixed rocker shaft and the need for only one cam phaser to variably control the open duration time of the valves, the present invention accrues significant manufacturing, mechanical, and cost advantages over prior art arrangements.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:
a are isometric and exploded isometric views, respectively, of a first embodiment of a CVVD system in accordance with the invention, shown in an assembly for operating a set of intake or exhaust valves in a four-cylinder engine head;
a are end elevation and isometric views, respectively, of the first embodiment shown in
a are end elevation and isometric views, respectively, of a third, embodiment of a CVVD system in accordance with the invention; and
a are end elevation and isometric views, respectively, of a fourth embodiment of a CVVD system in accordance with the invention.
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently-preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring to
Opening intake camshaft 102 includes a plurality of cam lobes 108 equal in number to the number of engine cylinders and spaced along the longitudinal axis 110 of the camshaft. Each cam lobe 108 is defined by a profile having a base circle portion 112, an ascending flank 114, a nose portion 116, and a descending flank 118. Journals 101 (in this case five) are also spaced along the longitudinal axis of opening intake camshaft 102 and rest on mating bearing surfaces 122 of base plate 103. Dowels 123 are provided to align base plate 103 with head 104. First end 124 of opening intake camshaft 102 further includes gear 126 fixed to its end. Gear 126 is rotatably coupled to the engine crankshaft (not shown) through a belt, chain, or gear mesh and is sized to rotate the opening camshaft a single revolution for every two revolutions of the crankshaft, as is known in the art. Second end 128 of opening intake camshaft further includes output gear 130 fixed to its end. Both gears 126, 130 are secured to ends 124, 128 to rotate with opening intake camshaft 102. While gear 130 is shown as a spur gear (
CVVD system 100 further includes closing intake camshaft 132 off-spaced from and parallel to opening intake camshaft 102. Closing intake camshaft 132 further includes a plurality of cam lobes 134 equal in number to the number of engine cylinders and spaced along the longitudinal axis 136 of the camshaft. Each cam lobe 134 is defined by a profile having a base circle portion 138, an ascending flank 140, a nose portion 142, and a descending flank 144. Journals 105 are also spaced along the longitudinal axis 136 of closing intake camshaft 132 and rest on mating bearing surfaces 148 of carrier modules 149. First end 150 of closing intake camshaft 132 terminates at the first bearing surface 148 in the row of bearing surfaces. Second end 152 of closing intake camshaft 132 further includes a cam phaser 154 having input gear 156 in meshing engagement with output gear 130 of opening intake camshaft 102.
The geared relationship between the opening camshaft and the phaser of the closing camshaft is only exemplary. Obviously, the phaser may be driven directly by the engine crankshaft in a manner similar to that just described for the opening camshaft, or by any other suitable means, for example, by an electric motor, to perform the same valve-closing phasing function.
Cam phaser 154 may be of a variety of types of phasers known in the art including a type known in the prior art as a “vaned” cam phaser. As such the phaser is used to selectively alter the phase angle between cam lobes 108, 134 of the opening intake camshaft and closing intake camshaft, respectively.
CVVD system 100 further includes a plurality of rocker subassemblies 160, equal in number to the number of cylinders in head 104, and pivotably mounted on elongate rocker pivot shaft 162. Axis 164 of rocker pivot shaft 162 is off-spaced from, but parallel to, and disposed between opening intake camshaft 102 and closing intake camshaft 132. The position of rocker pivot shaft 162 relative to head 104 is fixed. That is, unlike prior art variable valve actuating systems, the pivot point (axis 164) of rocker assembly 160 is not moved in order to achieve the desired variation in valve actuation.
Rocker subassembly 160 further includes rocker lever 165 having opening input arm 166, closing input arm 168 and output arm 170. Roller 172 is rotatably fastened to an end of opening input arm 166 for engagement with an associated opening intake camshaft lobe 108. Roller 174 is rotatably fastened to an end of closing input arm 168 for engagement with associated closing intake camshaft lobe 134. Rollers 172, 174 are preferably formed of hardened steel as is known in the art.
At a distal end of output arm 170 is actuating paddle 176. Paddle 176 is preferably formed into a compound arcuate shape. Preferably each paddle contact surface 178 is ground for smooth contact with center roller 180 of each roller finger follower 182. Roller finger follower 182, as is well known in the art, pivots at first end 184 about hydraulic lash adjuster 186 as a downward force is applied to center roller 180 of roller finger follower 182 to open intake valve 188 against valve return spring 190. As can be readily seen in
Torsional return spring 194 is connected at end 194a to rocker lever 165 and at end 194b to carrier module 149 to thereby bias rocker lever 165 in a counterclockwise direction so as to maintain contact between rollers 172, 174 and one or both of cam lobes 108, 134 during operation of the engine. While return spring 194 is shown as a torsional spring in
As mentioned previously, gear 126 of opening intake camshaft 102 is driven by a chain, belt or gearing from an engine's crankshaft in a 2:1 rotational ratio (2 revolutions of the crankshaft for every one revolution of the camshaft 102). Since output gear 130 of opening intake camshaft 102 and input gear 156 of cam phaser 154 are of the same diameter and have the same number of teeth, closing intake camshaft 132 is driven from opening intake camshaft 102 in a 1:1 rotational ratio. And, since gears 126, 130 are in direct mesh, closing intake camshaft 132 rotates in a counter direction 193 from the direction 189 of opening intake camshaft 102. Recalling that opening intake camshaft 102 is rotationally connected to closing intake camshaft 132 through cam phaser 154, a signal received by the cam phaser from a controller (not shown) causes the angular position of lobe 134 of the closing intake camshaft to shift relative to lobe 108 of the opening camshaft, from its default position shown in
Referring now to
Following curve 198 in
When delaying of the closing event of intake valve 188 is desired, a signal from the engine controller directs cam phaser 154 to retard the rotational position of closing intake camshaft 132 relative to opening intake camshaft 102. This causes a portion of descending flank 144 of closing intake cam lobe 134 to come into contact with roller 174 and to take over control of the movement of rocker sub assembly 160 from opening intake cam lobe 108. As can be seen by resulting curve 198, roller 172 remains in contact with lobe 108 almost through the entire opening and closing event. However, since the phasing of closing intake camshaft 132 has been retarded by the cam phaser, roller 174 comes in contact with descending flank 144 of lobe 134 at Point A (phaser retards lobe 134 by 20°) and, from that point until valve 188 is closed (curve 198a), closing intake cam lobe 134 takes over from opening intake cam lobe 108 and keeps intake valve 188 open to about 140 cam angle degrees (point 195 in
For clarity of presentation,
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While the invention has been described as applicable to intake valves, it is understood that the invention's application need not be so limited.
While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims.
This patent application claims the benefit of U.S. Provisional Application No. 60/847,784, filed Sep. 28, 2006.
The present invention was supported in part by U.S. Government Contract No. DE-FC26-05NT42483. The United States Government may have rights in the present invention.
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Number | Date | Country | |
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20080078346 A1 | Apr 2008 | US |
Number | Date | Country | |
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60847784 | Sep 2006 | US |